Articles such as food, medicine, a touch panel, an organic EL (electroluminescence) device, an inorganic EL device, a solar cell, and electronic paper are altered and deteriorated by moisture and oxygen in the atmosphere, thereby losing their value for sale. Therefore, packing or sealing is utilized by using a film having a so-called gas barrier property for preventing transmission of moisture and oxygen in the atmosphere.
However, the grade of the barrier property required for the gas barrier film for protecting and maintaining the properties of the various articles as mentioned above depends on the kinds of those articles. For example, a very high grade of the barrier property is required for a gas barrier film used for an organic EL device. As compared to this, however, a gas barrier film not having such a high grade of the barrier property can be used for protecting goods such as food and medicine.
In the meantime, while the organic EL display device draws attention as a light-emitting display, the organic molecular layers such as an organic light-emitting layer, an electron transport layer and a positive-hole transport layer have their fatal weak point that they react with moisture and oxygen in the atmosphere and are degraded.
As it stands now, therefore, the. organic EL device is formed on a glass substrate which moisture and oxygen hardly penetrate and is covered with a sealing can or glass so as to extend the device lifetime.
In this case, there is a cost problem caused by the sealing can or sealing glass. As a measure to solve the problem, a so-called thin-film sealing technique is desired, in which a gas barrier layer is formed with a thin film in place of the sealing can or sealing glass.
From a technical viewpoint of a display device that is flexible and lightweight and expected as a future article, it is also desirable to develop a display device in which an organic EL layer is formed on a plastic film without using a glass substrate.
For that purpose, it is necessary to realize a gas barrier film for preventing transmission of moisture and oxygen harmful to the EL layer and realize a thin-film sealing technique for protecting the organic EL device formed on the barrier film.
As technical problems in developing a flexible organic EL device, therefore, it is first necessary to realize a technique for forming a film that adheres tightly to a plastic film and has a high barrier property, and it is secondly necessary to realize a thin-film sealing technique using a gas barrier film for protecting the organic EL layer that is sensitive to gas, heat and plasma and then is liable to be damaged.
As an attempt to solve these problems, a patent literature 1 of Japanese National Paten Publication No. 2002-532850 discloses an example of a method for forming a barrier film. In the method discloses by this patent literature 1, a barrier film is formed with a stacked-layer structure of polymer layers and inorganic material layers. The polymer layers are formed by vapor deposition of monomers (typically, monomers containing acrylate) and subsequent photo polymerization due to ultraviolet irradiation. Further, as the inorganic material layers, layers such as of silica, alumina, titania, indium oxide, tin oxide, aluminum nitride, or silicon nitride are formed by sputtering or the like. Then it is considered that the polymer layers are used mainly for planarization of the organic EL device and fill defects in the inorganic material layers, while the inorganic material layers show a barrier property.
A problem in the barrier film according to patent literature 1 is that the film must be made as thick as about 10 micrometers by alternately stacking many times the polymer layers and the inorganic material layers in order to obtain a high barrier property. Further, since various treatment processes such as vacuum evaporation, photo polymerization and sputtering and then apparatus for the processes are required for production of the barrier film, the manufacturing facilities becomes complicated and the production cost is increased. Furthermore, since the polymer layers themselves hardly have a barrier property and the inorganic material layers themselves usually become porous and polycrystalline particle state, it is difficult to prevent invasion of moisture and oxygen particularly through the side surfaces of the organic EL device.
In the meantime, a patent literature 2 of Japanese Patent Laying-Open No. 2008-155585 discloses a gas barrier film including a first, a second and a third organic-inorganic hybrid layer. Each of these organic-inorganic hybrid layers contains carbon, silicon, nitrogen, and hydrogen that have been intentionally introduced. In this case, the first and third organic-inorganic hybrid layers deposited by plasma CVD (chemical vapor deposition) have greater carbon composition ratios as compared with the second organic-inorganic hybrid layer deposited by Cat-CVD (catalyst CVD). On the other hand, the second organic-inorganic hybrid layer is set to have greater composition ratios of silicon and nitrogen as compared with the first and third hybrid layers.
Incidentally, it should be noted that while the organic-inorganic hybrid material means a combination of organic material and inorganic material, the material called particularly as the organic-inorganic hybrid material is in a mixed state in a nano range or a molecular range differently from a simple mixture such as the conventionally known composite material (refer to a patent literature 3 of Japanese Patent Laying-Open No. 2005-179693, for example).